This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The formation of calcium carbonate (chalk) from a saturated calcium bicarbonate solution (i.e. hard water) proceeds at neutral pH (which is typical for the formation of minerals in living animals or sea water) via a very uncommon liquid intermediate, which is remarkable stable and nanosized. The goal of this project is to characterize in situ the mechanism and the intermediate calcium compounds which occur during this precipitation. The employed levitated droplet technique allows an in situ monitoring of the homogenous crystallization of calcium carbonate while avoiding any foreign phase boundaries that may influence the precipitation process by heterogeneous nucleation. Understanding the basics of classical biomineral formation is essential for biomimetic or bio-inspired new materials and for the development of bone implants and bone/teeth substitute materials.